Thor kinda breaks my heart in this scene. His brother is about to use him to “test if gods are immortal”, and he just stands there in stunned silence. He doesn’t threaten Loki or try to reason with him. But he does cry. (it’s hard to tell from the blurry cam gifs)
YES THANK YOU GOD
Everyone always focuses on leaky Loki and him being the one to be shedding the lone manly tear in the scenes like this (with good reason, of course), but I don’t think we’ve ever seen Thor as lost or as resigned as he is here.
He’s not pleading or shouting or raging, he’s just silently accepting the fact that his brother has succumbed so completely to whatever madness the Tesseract and Thanos have inflicted on him.
I think it also has a lot to do with the fact that he blames himself for what’s happened to his brother. Because, all things considered, a great deal of Loki’s anger and sense of betrayal stems from him.
So this moment is him deciding to allow Loki to have this. To have a victory over the mighty Thor. To step out of the shadows once and for all, regardless of whether or not the cost may be his own life.